The present invention relates to a resist composition used in production of semiconductor elements, etc., more particularly, to a resist composition used in formation of a positive type pattern using ultraviolet light, particularly deep ultraviolet light having a wavelength of not higher than 300 nm, for instance, KrF excimer laser light, as an exposure energy source.
With a recent trend toward higher density integration of semi-conductor devices, an energy source for exposure means used for fine working, particularly photolithography, becomes to have shorter and shorter wavelengths. Now use of deep ultraviolet light (wavelength of not higher than 300 nm), KrF excimer laser light (wavelength of 248.4 nm), etc. has been started. However, there has not yet been available a resist composition having high applicability to a technology for production in large scale with the use of this kind of short wavelength exposure light.
As a resist composition for KrF excimer laser light and deep ultraviolet light as the exposure source, a chemical amplified type resist composition proposed by H. Ito et al has generally been used and improved for reducing exposure energy amount [H. Ito et al, Polym. Eng. Sci., 23, 25 1012 (1983)].
Many reports have been published concerning chemical amplified type resist compositions, and those compositions have been accompanied with many problems to be solved from a view point of practical applicability.
Namely, in the reports at early development stage [e.g. JP-B 2-27660 (U.S. Pat. No. 4,491,628); JP-A 62-115440 (U.S. Pat. No. 4,603,101); JP-A 2-25850; Y. Jian et al Polym. Mater. Sci. and Eng., 66, 41(1992),etc.], polymers used therein were phenolic ether type polymers such as poly(p-tert-butoxycarbonyloxystyrene), poly(p-tert-butoxystyrene), poly(p-tert-butoxycarbonyloxy-xcex1-methylstyrene), poly(p-tert-butoxy-xcex1-methylstyrene), poly(tert-butyl p-isopropenylphenoxyacetate), poly(p-tert-butoxycarbonyloxystyrene/sulfone), poly(p-tetrahydropyranyloxystyrene), poly[p-(1-methoxyethoxy)styrene) and poly([p-(1-phenoxyethoxy)styrene], but all of these polymers are poor in their adhesion to substrates, easily peeled off from the substrate upon development, and further poor in heat resistance. Therefore, the resist compositions containing those polymers have such a defect as giving no good pattern. In the case of resist compositions using carboxylic acid type polymers such as poly(tert-butyl p-vinylbenzoate) and poly(tetrahydropyranyl p-vinylbenzoate), there is such a defect in that transmittance around 248.4 nm is not satisfactory because of the benzoyl group and thus the resolution is not good. In the case of resist compositions using poly(tert-butyl methacrylate), there are problems of poor heat resistance of polymer and poor dry-etching resistance.
Additionally, resist compositions using silicon-containing polymers have been disclosed [e.g. JP-B 3-44290], but in cases of using poly(p-trimethylsilyloxystyrene) and poly(p-tert-butyldimethylsilyloxystyrene), there are found such defects as low sensitivity, incomplete removal by ashing due to the silicon contained therein, etc., and thus they are difficult to realize a practical use.
With a development of the technology, there have been reported chemical amplified type resist compositions in which the above defects are improved by using poly(p-tert-butoxycarbonyloxystyrene/p-hydroxystyrene) [JP-A 2-209977; JP-A 3-206458], poly(p-tetrahydropyranyloxystyrene/p-hydroxystyrene) [Japanese Patent No. 2675138 (EPC No. 342498); JP-A 2-161436; JP-A 3-83063] and poly(p-tert-butoxystyrene/p-hydroxystyrene) [JP-A 2-62544; JP-A 4-211258 (U.S. Pat. No. 5,350,660, EPC No. 440374).]
However, any of the resist compositions using those polymers cannot attain the required resolution ability, nor overcome the problem of delay time which has been discussed in practical application [change in dimension and deterioration of the pattern shape during the time from coating of the resist to the light exposure or during the time from the light exposure to the heat treatment (PEB)] and the problem of substrate dependency [SiO2, Si3N4, Ti3N4, BPSG or polysilicon have been used as the semiconductor substrate, and the pattern shape becomes bad depending upon the kind of the substrate material].
Thereafter, resist compositions using polymers in which an acetal group or a ketal group is introduced as a protecting group [e.g. poly(p-1-methoxyethoxystyrene/p-hydroxystyrene)] and a photoacid generator such as triphenylsulfonium salt derivative and diphenyliodonium salt [e.g. JP-A 2-161436; JP-A 4-219757 (EPC No. 447868); JP-A 5-281745 (EPC Publication No. 553737); JP-A 3-282550] have been reported. However, they are accompanied with such problems as generation of scum (undissolved parts generated during development: they cause a problem of transcription to the under substrate plate upon etching), a substrate dependency and delay time. Additionally, JP-A 5-249682 (EPC Publication No. 520642)], discloses a resist composition comprising a polymer such as poly(p-1-ethoxyethoxystyrene/p-hydroxystyrene), poly(p-1-methoxy-1-methylethoxystyrene/p-hydroxystyrene), poly(p-1-ethoxyethoxystyrene/p-hydroxystyrene/methyl methacrylate) or poly(p-1-ethoxyethoxystyrene/p-hydroxystyrene/fumaronitrile), and a diazodisulfone compound as a photoacid generator, and JP-A 8-253528 discloses a resist composition comprising poly(p-1-tert-butoxyethoxystyrene/p-hydroxystyrene) and a diazodisulfone compound as a photoacid generator.
Though those resist compositions are excellent in many aspects such as resolution ability and delay time and so on, they are still accompanied with such problems as poor substrate dependency and generation of scum.
JP-A 8-15864 (EPC Publication No. 679951, U.S. Pat. No. 5,736,296), JP-A 8-262721, JP-A 9-127698, JP-A 9-90639 resist compositions containing a mixture of two kinds of polymers , poly(p-1-ethoxyethoxystyrene/p-hydroxystyene) and poly(p-tert-butoxycarbonyloxystyrene/p-hydroxystyrene), and one or more diazodisulfone compounds as a photoacid generator. JP-A 9-160244 discloses a composition containing a mixture of two kinds of polymers, poly(p-1-ethoxyethoxystyrene/p-hydroxystyrene) and poly(tert-butoxystyrene/p-hydroxystyrene), and one or more photoacid generators. JP-A 10-97074 discloses a composition containing two kinds of polymers, poly(p-1-ethoxyethoxystyrene/p-hydroxystyrene) and poly(p-tetrahydropyranyloxystyrene/p-hydroxystyrene) and one or more photoacid generators. These compositions are accompanied with many problems such as poor in resolution ability, DOF and side-wall shape which are required for the characteristics in recent resolution degree of 0.20 to 0.15 xcexcm L/S.
JP-A 9-160246 discloses a resist composition containing poly(p-1-ethoxyethoxystyrene/p-tert-butoxystyrene/p-hydroxystyrene), a compound having a molecular weight of 1000 to 3000 wherein hydrogen atoms of phenolic hydroxy groups are partially substituted with acid-labile group, as a dissolution-inhibitor and an oinum salt as a photoacid generator. JP-A 10-48826 discloses a resist composition in which p-hydroxystyrene type polymer containing p-hydroxystyrene monomer units protected with an acetal group (e.g. an 1-ethoxyethoxy group) and p-hydroxystyrene type polymer containing p-hydroxystyrene monomer units protected with an alkoxy group (e.g. a tert-butoxy group) whose weight average molecular weight is less than the former polymer are co-used and one or two kinds of photoacid generators are used in combination of the polymers. However, these compositions are also accompanied with many problems concerning poor DOF, side-wall shape, delay time, substrate dependency, poor storage stability and the like contrary to required characteristics in recent resolution degree of 0.20 to 0.15 xcexcm pattern size.
Still further, JP-A 9-274320 and JP-A 10-53621 disclose resist compositions containing poly(p-1-ethoxyethoxystyrene/p-hydroxystyrene/p-tert-butoxycarbonyloxystyrene) or poly(p-1-ethoxyethoxystyrene/p-hydroxystyrene/p-tert-butoxystyrene) and photoacid generator composed of a mixture of a diazodisulfone compound and an onium salt, substantially containing no aromatic rings or aliphatic multi-rings as counter ions. However, these compositions are also accompanied with such problems as poor DOF, side-wall shape, delay time and the like contrary to required characteristics in recent resolution degree of 0.20 to 0.15 xcexcm pattern size.
As mentioned above, chemical amplified type resist compositions have been improved in their poor heat resistance of the polymer, poor adhesion to a substrate material and poor transmittance around 248.4 nm which had been found in the early stage of the development. But these compositions are still now accompanied with such problems as poor resolution ability, change in pattern size with the lapse of time, deterioration of pattern shape, poor DOF, footing and scum remained in the pattern, roughness in side walls of the pattern and the like. Thus, practically applicable resist compositions in which the above problems are solved have strongly been desired.
It is an object of the present invention to provide a practically applicable resist composition which shows high transparency against ultraviolet light, particularly deep ultraviolet light having a wavelength of 300 nm or less, KrF excimer laser light, and the like, shows high sensitivity to exposures by those light sources and to irradiation with electron beams, soft X-ray, etc., is excellent in heat resistance and adhesion to substrates, has high resolution, is capable of giving highly precious patterns without causing pattern size change with the lapse of time, shows high storage stability, has a wide DOF and good mask linearity, shows no substrate dependency, and is capable of forming rectangular pattern forms with less roughness in the side walls without causing footing and scum.
The present invention provides a chemically amplified resist composition comprising
(a) two kinds or more of polymers which become alkali-soluble by an action of an acid and represented by the formula: 
wherein R1 and R2 are independently a hydrogen atom or a methyl group; R3 and R4 are independently a hydrogen atom, a straight-chain, branched or cyclic alkyl group having 1 to 6 carbon atoms, a straight-chain, branched or cyclic haloalkyl group having 1 to 6 carbon atoms, a phenyl group which may have one or more substituents, or R3 and R4 can together form a methylene chain, provided that both R3 and R4 cannot be hydrogen atoms at the same time; R5 is a straight-chain, branched or cyclic alkyl group having 1 to 10 carbon atoms, a straight-chain, branched or cyclic haloalkyl group having 1 to 10 carbon atoms, or an aralkyl group; R22 is an esterified carboxyl group or an aryl group which may have one or more substituents; m and n are independently an integer; and j is zero or an integer, provided that 0.10xe2x89xa6(m+j)/(m+n+j)xe2x89xa60.90, and 0xe2x89xa6j/(m+n+j)xe2x89xa60.25,
(b) at least one compound of the formula: 
wherein R8 is a branched or cyclic alkyl group having 3 to 8 carbon atoms; and R9 is a straight-chain, branched or cyclic alkyl group having 1 to 8 carbon atoms, or an aralkyl group, and
at least one compound selected from the group consisting of a compound of the formula: 
wherein R10 , R11 and R12 are independently a hydrogen atom, a halogen atom, a straight-chain, branched or cyclic alkyl group having 1 to 6 carbon atoms, a straight-chain, branched or cyclic alkoxy group having 1 to 6 carbon atoms, or a phenylthio group; R13 is a 1-naphthyl group, a 2-naphthyl group, a 10-camphoryl group, a pyridyl group, or a group of the formula: 
wherein R14 and R15 are independently a hydrogen atom or a halogen atom; and R16 is a hydrogen atom, a halogen atom, a straight-chain, branched or cyclic alkyl group having 1 to 12 carbon atoms, a straight-chain or branched alkoxy group having 1 to 4 carbon atoms, or a trifluoromethyl group, and a compound of the formula: 
wherein R17 and R18 are independently a hydrogen atom, a straight-chain or branched alkyl group having 1 to 4 carbon atoms, a straight-chain or branched alkoxy group having 1 to 4 carbon atoms; and R19 is a 1-naphthyl group, a 2-naphthyl group, a 10-camphoryl group, a phenyl group, or a phenyl group substituted with one or more, the same or different, straight-chain, branched or cyclic alkyl groups having 1 to 12 carbon atoms, and
(c) a solvent dissolving the components (a) and (b).